John asks 'why not Paul'. Kevin Drum has put together a long list of reasons, in short:
Can we talk? Ron Paul is not a charming oddball with a few peculiar notions. He's not merely "out of the mainstream." Ron Paul is a full bore crank. In fact he's practically the dictionary definition of a crank: a person who has a single obsessive, all-encompassing idea for how the world should work and is utterly blinded to the value of any competing ideas or competing interests.Read the article for the full list.
The problem with Paul is not just the fact that he wrote a blatantly racist newsletter for many years and is obviously lying about it. Just as the problem with Cain was not just the fact that he was unable to give a credible explanation of the allegations of sexual harassment.
At least a Bachmann, Perry or Cain might be content to be (mostly) a figurehead. Paul would not be a figurehead.
None of the GOP contenders is an attractive nominee and that is not an accident of chance. It is a consequence of the politics that the GOP has been engaging in the past 12 years. Romney, Santorum and Gingrich are the very best, the finest that the party can produce. This is not a party fielding its B team while their superstars sulk in their tent, these are the best people they can put on the field.